Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1162357Ab3DESLw (ORCPT ); Fri, 5 Apr 2013 14:11:52 -0400 Received: from mail-ie0-f182.google.com ([209.85.223.182]:63121 "EHLO mail-ie0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1162306Ab3DESLu convert rfc822-to-8bit (ORCPT ); Fri, 5 Apr 2013 14:11:50 -0400 MIME-Version: 1.0 In-Reply-To: <1365181075-22540-1-git-send-email-piastry@etersoft.ru> References: <1365181075-22540-1-git-send-email-piastry@etersoft.ru> Date: Fri, 5 Apr 2013 22:11:50 +0400 X-Google-Sender-Auth: exfembZPbdHEhJFfE2VyVOhog5w Message-ID: Subject: Re: [PATCH v4 0/7] Add O_DENY* support for VFS and CIFS/NFS From: Pavel Shilovsky To: linux-kernel@vger.kernel.org Cc: linux-cifs , linux-fsdevel , Linux NFS Mailing list , wine-devel@winehq.org Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3828 Lines: 50 2013/4/5 Pavel Shilovsky : > Main changes from the previous one: > 1) O_DENYMAND is removed, sharelock mount option is introduced. > 2) Patch fcntl.h and VFS patches are united into one. > 3) flock/LOCK_MAND is disabled for sharelock mounts. > > This patchset adds support of O_DENY* flags for Linux fs layer. These flags can be used by any application that needs share reservations to organize a file access. VFS already has some sort of this capability - now it's done through flock/LOCK_MAND mechanis, but that approach is non-atomic. This patchset build new capabilities on top of the existing one but doesn't bring any changes into the flock call semantic. > > These flags can be used by NFS (built-in-kernel) and CIFS (Samba) servers and Wine applications through VFS (for local filesystems) or CIFS/NFS modules. This will help when e.g. Samba and NFS server share the same directory for Windows and Linux users or Wine applications use Samba/NFS share to access the same data from different clients. > > According to the previous discussions the most problematic question is how to prevent situations like DoS attacks where e.g /lib/liba.so file can be open with DENYREAD, or smth like this. That's why extra mount option 'sharelock' is added for switching on/off O_DENY* flags processing. It allows us to avoid use of these flags on critical places (like /, /lib) and turn them on if we really want it proccessed that way. > > So, we have 3 new flags: > O_DENYREAD - to prevent other opens with read access, > O_DENYWRITE - to prevent other opens with write access, > O_DENYDELETE - to prevent delete operations (this flag is not implemented in VFS and NFS part and only suitable for CIFS module), > > The patchset avoid data races problem on newely created files: open with O_CREAT can return the -ETXTBSY error for a successfully created file if this files was locked with a deny lock by another task. Also, it turns flock/LOCK_MAND capability off for mounts with 'sharelock' option. This let us not mix one share reservation approach with another. > > The #1 patch adds flags to fcntl and implements VFS part. The patches #3, #4, #5 are related to CIFS-specific changes, #6 and #7 describe NFS and NFSD parts. > > The preliminary patch for Samba that replaces the existing use of flock/LOCK_MAND mechanism with O_DENY* flags: > http://git.etersoft.ru/people/piastry/packages/?p=samba.git;a=commitdiff;h=173070262b7f29134ad6b2e49a760017c11aec4a > > The future part of open man page patch: > > ----- > O_DENYREAD, O_DENYWRIYE, O_DENYDELETE - used to inforce a mandatory share reservation scheme of the file access. If these flag is passed, the open fails with -EBUSY in following cases: > 1) if O_DENYREAD flag is specified and there is another open with O_DENYMAND flag and READ access to the file; > 2) if O_DENYWRITE flag is specified and there is another open with O_DENYMAND flag and WRITE access to the file; > 3) if READ access is requested and there is another open with O_DENYMAND and O_DENYREAD flags; > 4) if WRITE access is requested and there is another open with O_DENYMAND and O_DENYWRITE flags. Should be without O_DENYMAND (copy-and-paste issue, sorry): 1) if O_DENYREAD flag is specified and there is another open with READ access to the file; 2) if O_DENYWRITE flag is specified and there is another open with WRITE access to the file; 3) if READ access is requested and there is another open with O_DENYREAD flags; 4) if WRITE access is requested and there is another open with O_DENYWRITE flags. -- Best regards, Pavel Shilovsky. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/